The replication process of the parvovirus H-1 is being analyzed and H-1 is being applied as a probe for the study of eukaryotic DNA replication. An understanding of the unusual dependence of parvovirus DNA synthesis for a late S phase event should provide insight into the control of cell DNA replication. Isolation of more conditional lethal mutants of H-1 will aid the genetic analysis of the virus and the discrimination of those functions specified by the virus from the host cell functions required for replication of the virus. The mechanism of replication of the ends of the linear viral replicon should provide insight into the enzymology of the replication of the ends of the eukaryotic chromosomes. H-1 RF DNA and variants of it are being tested for their suitability in the construction of a eukaryotic plasmid.